Carbon dioxide waters in Iceland: A natural analogue to CO2 sequestration in basaltic aquifers

Carbon dioxide rich waters are common in particular geological settings worldwide. In Iceland, they occur in the volcanically active non-rifting zones. They form by mixing of magmatic CO2 with surface, non-thermal or geothermal groundwater. CO2-waters also form in volcanic geothermal areas by mixing of CO2-rich vapor with surface or groundwater. CO2-waters are highly reactive, producing fluids that differ chemically from other surface and groundwaters, with differences decreasing with increasing temperatures. In particular, CO2-waters are higher in Ca, Mg and Fe, as wells as many trace elements, some of which affect water quality, including As, Ba, Mn and Sr. The CO2-waters are generally close to saturation with amorphous silica and calcite, often with ankerite, siderite and dolomite and occasionally with magnesite and rhodochrosite, but invariably under-saturated with strontianite and witherite. The data presented here are useful for assessing the impact of CO2 sequestration on groundwater quality in basalt aquifers.